1. Field of the Invention
The invention concerns a wind power installation for producing a sinusoidal ac voltage comprising a generator having a generator rotor and a generator stator, a rotor unit with rotor blades which is connected to the generator rotor, and power transmission means for the transmission of electrical power from the non-rotating part of the wind power installation to the rotor unit.
2. Description of the Related Art
In the case of wind power installations it is necessary for power to be transmitted from the non-rotating part to the rotating part, for various purposes. For example, in the case of an electromagnetically excited synchronous generator, a direct current is required as the exciter current for the pole wheel, and for rotor blade adjustment by means of suitable electric motors that also requires electrical power. At the present time that power is transmitted from the non-rotating part of the wind power installation to the rotating part by means of slip rings. Slip rings however basically suffer from the disadvantage that losses occur by virtue of the friction involved, that is to say the level of efficiency is reduced, a large amount of noise is generated, and in particular they suffer from a high level of wear, and therefore need to be repaired or have to be replaced from time to time. In addition electrical flash-overs can occur at such slip rings. They are even further promoted with increasing operating time, due to the abrasion of particles.
DE 198 01 803 A1 discloses an electrical rotational machine with a stationary stator and a rotatable rotor. In that case they have a stator transformer winding and a rotor transformer winding respectively, wherein the transformer windings form an electrical transformer and are each designed for operation with alternating current. By means of the transformer windings a three-phase current which is fed in from a supply network can be transmitted to the rotating part of the wind power installation, and is then fed to the three-phase current, generator winding disposed in the stator of the generator of the wind power installation, for excitation purposes.
U.S. Pat. No. 5,770,909 describes a synchronous machine for electrically operated vehicles, with which the power of the generator is to be optimised for all travel conditions, in particular over a rotary speed range of from zero to several thousand revolutions per minute.